1. Field of the Invention
The present invention relates to a method for manufacturing an indium-tin-iron type catalyst which is used for producing carbon nanocoils that have an external diameter of 1000 nm or less and more particularly to a method for manufacturing an indium-tin-iron type catalyst for use in the production of carbon nanocoils which allows inexpensive mass production by utilizing metal-containing organic compounds and an organic solvent.
2. Prior Art
The history of carbon nanocoils in which the external diameter of the coil is on the order of nanometers is relatively brief.
In 1994, Amelinckx et al. (Amelinckx, X. B. Zhang, D. Bernaerts, X. F. Zhang, V. Ivanov and J. B. Nagy, SCIENCE, 265 (1994) 635) succeeded in producing carbon nanocoils. While carbon microcoils discovered in the past have an amorphous structure, it has been ascertained that carbon nanocoils have a graphite structure. Various types of carbon nanocoils have been prepared, and the smallest coil external diameter achieved so far is extremely small, i.e., approximately 12 nm. However, the coil yield is small, and such a method cannot be utilized in industrial production. Accordingly, there has been a demand for a more efficient method of manufacture of nanocoils.
In the manufacturing method used by the above researchers, a metal catalyst such as Co, Fe or Ni is formed into a very fine powder, the area in the vicinity of this catalyst is heated to a temperature of 600 to 700xc2x0 C., an organic gas such as acetylene or benzene is caused to flow through so that the gas contacts the catalyst, and then the organic molecules are broken down. The carbon nanocoils that are produced have various shapes, and these shapes are merely produced at random.
In 1999, Li et al. (W. Li, S. Xie, W. Liu, R. Zhao, Y. Zhang, W. Zhou and G. Wang, J. Material Sci., 34 (1999) 2745) succeeded anew in producing carbon nanocoils. In the method used by these researchers, a catalyst formed by covering the surface of a graphite sheet with iron particles is placed in the center of the reaction vessel, and the area in the vicinity of this catalyst is heated to 700xc2x0 C. by means of a nichrome wire. A mixed gas consisting of 10% acetylene and 90% nitrogen by volume is then caused to flow through so that the gas contacts the catalyst. However, in this manufacturing method as well, the rate of coil production is small, and thus this method is extremely inadequate as an industrial mass production method.
Under such conditions, the present inventors discovered a method for the mass production of carbon nanocoils at the end of 1999. This method is disclosed in Japanese Patent Application No. 11-377363.
In this method, an indium-tin-iron type catalyst is placed inside a reaction vessel, the area in the vicinity of this catalyst is heated to a temperature that is equal to or greater than the temperature at which a hydrocarbon gas is broken down by the catalyst, and a hydrocarbon gas is caused to flow through so as to contact the catalyst, thus causing the growth of carbon nanocoils on the surface of the catalyst. The production rate of this method is a maximum of 95% or greater. Thus, this method allows the mass production of carbon nanocoils.
The core of the above-described manufacturing method lies in the indium-tin-iron type catalyst. The lowering of the manufacturing cost of carbon nanocoils is determined by how inexpensively the indium-tin-iron type catalyst can be provided. The present inventors prepared an indium-tin-iron type catalyst by vacuum-evaporating an iron film on a commercially marketed ITO (indium-tin-oxide) substrate. Since the ITO substrate is expensive, and since the catalyst is prepared by the vacuum evaporation of iron, which is a method unsuited to mass production, the resulting indium-tin-iron type catalyst is extremely expensive.
ITO substrates are transparent substrates which consist of an indium oxide and tin oxide and possess electrical conductivity and a high light transmissivity. Such substrates have been adapted for practical use as industrial materials which are indispensable in opto-electronics, etc. The high cost of such ITO substrates is attributable to the method used to manufacture these substrates. There are three main manufacturing methods.
The first method is a spray method. In this method, a mixed solution consisting of InCl3, SnCl4, H2O, HCl and an alcohol is sprayed onto a substrate, and this substrate is then baked at approximately 500xc2x0 C. In this method, chlorine type gases are generated in the baking process. Thus, problems such as contamination of the environment and corrosion of the apparatus, etc. occur.
The second method is a CVD (chemical vapor deposition) method. In this method, an In chelate and dibutyltin diacetate are used as raw materials, and manufacture is accomplished by CVD method using N2 gas as a carrier at a substrate temperature of approximately 500xc2x0 C. Since this method is performed inside a sealed vessel, it is unsuitable for mass production.
The third method is a vacuum evaporation method. In this method, In and Sn are used as evaporation sources, and vacuum evaporation for formation is performed at a substrate temperature of approximately 400xc2x0 C. Since the operation is performed inside a vacuum apparatus, it is not suitable for mass production.
Thus, since conventional indium-tin-iron type catalysts are manufactured by the vacuum evaporation of iron on an expensive ITO substrate, the manufacturing cost is high, and then mass production is impossible. As a result, the inexpensive mass production of carbon nanocoils is considered impossible.
Accordingly, the object of the present invention is to realize the mass production of carbon nanocoils and a reduction in the cost of carbon nanocoils by establishing an inexpensive method for the mass production of an indium-tin-iron type catalyst.
The above object is accomplished by the unique manufacturing method of the present invention for manufacturing an indium-tin-iron type catalyst which is used to produce carbon nanocoils that have an external diameter of 1000 nm or less, wherein the manufacturing method comprises:
a first process that forms an organic solution by mixing an indium-containing organic compound and a tin-containing organic compound with an organic solvent,
a second process that forms an organic film by coating a substrate with the thus obtained organic solution,
a third process that form an indium-tin film by baking this organic film, and
a fourth process that forms an iron film on the surface of the indium-tin film.
In the above method, the indium-tin film is a mixed film of an indium oxide and a tin oxide.
Furthermore, in the above fourth process, the iron film on the surface of the indium-tin film is formed by electroplating.
The above object is further accomplished by another unique manufacturing method of the present invention for manufacturing an indium-tin-iron type catalyst which is used to produce carbon nanocoils that have an external diameter of 1000 nm or less, wherein the manufacturing method comprises:
a first process that forms an organic solution by mixing an indium-containing organic compound, a tin-containing organic compound and an iron-containing organic compound with an organic solvent,
a second process that forms an organic film by coating a substrate with the thus obtained organic solution, and
a third process that forms an indium-tin-iron film by baking the organic film.